The role of the cell membrane, ion fluxes and cyclic AMP in control of hormone secretion is being studied. Release of zymogen granules by the exocrine pancreas is being studied as a Ca ion dependent system in which cyclic AMP is not involved. Secretion has been stimulated by the Ca ion ionophore A23187 although the Ca ions of physiological importance for stimulus-secretion coupling appears released from intracellular sites. Ca ions release is being studied by use of CA 45 ions efflux measurements. Pharmacologic agents affecting Ca ion binding and transport including La ion, tetracaine and D600 are being studied. Pancreatic enzyme release has also been found to be Na ion dependent and the role of Na ion is being studied. The role of microtubules in pancreatic secretion (exocytosis) and thyroid hormone secretion (endocytosis) is being studied. Preliminary work is in progress to extend these types of studies to the mechanism of LH release by the anterior pituitary gland.